A method for preparing Cr-containing nickel-based powder metallurgy material based on high-current pulsed electron beam surface strengthening

Abstract

The present invention discloses a method for preparing a Cr-containing nickel-based powder metallurgy material with a surface strengthened by a high-current pulsed electron beam. First, pure chromium and pure nickel powders are mixed into a Ni-21Cr mixed powder in a mass ratio of 79:21; a ball mill is used to mix the mixture to obtain a uniform powder; the powder is then pressed into shape using a mold, and then sintered in a sintering furnace; finally, the sintered sample is irradiated several times with a high-current pulsed electron beam to obtain a dense surface-strengthened Ni-Cr powder metallurgy sample. This method solves the two main problems of nickel-based materials prepared by existing methods, namely low hardness and poor wear resistance. In addition, the method has low production cost, simple operation, and a short process cycle, and can improve the surface properties of nickel-based materials, thereby extending their service life.

Description

Technical Field

[0001] The invention relates to a method for preparing a powder metallurgy material, in particular to a method for preparing a Cr-containing nickel-based powder metallurgy material. Background Art

[0002] Nickel-based alloys are typical materials used in high-temperature environments such as combustion power systems. The service environment is complex and harsh, and failure behavior is often the result of the combined effect of multiple factors, such as fatigue, creep, oxidation and thermal corrosion.

[0003] The surface of conventional powder metallurgy sintered samples is not dense, but loose and porous, resulting in poor strength. Furthermore, binary alloys formed by metallurgical sintering are subject to solubility limitations, meaning that equilibrium processing methods do not easily form supersaturated solid solutions.

[0004] High-current pulsed electron beam (HCPEB) is a newly emerged energetic beam surface modification technology that has attracted extensive attention from material scientists. 8 ~10 9 W / cm 2 ) is instantaneously deposited on the material surface, causing the irradiated material surface to simultaneously heat, melt, and rapidly solidify. This causes the surface layer to melt and cool, ultimately forming a remelted layer. Furthermore, phase transformation, grain refinement, and surface composition homogenization are all possible. Previous research has shown that surface treatments such as vapor deposition, thermal spraying, laser surfacing, and ion beam implantation are widely used for material surface modification. However, these methods often suffer from a series of issues, including high cost, complex procedures, long cycle times, and low efficiency. HCPEB surface treatment technology is an effective way to improve the mechanical properties of materials.

[0005] The addition of Cr to Ni-Cr alloys significantly improves their sulfidation capacity, electrical conductivity, and high-temperature oxidation resistance, while reducing the temperature coefficient of resistance (TCR). Consequently, they possess excellent heat resistance, high operating temperatures, high strength, and high-temperature corrosion resistance. They can be used as thermocouples, high-elasticity alloys, electric heating alloys, and precision resistance alloys. Therefore, the development of electron beam surface treatment processes is of great value for the application of nickel-based materials. Summary of the Invention

[0006] Purpose of the invention: In view of the above existing technologies, a surface strengthening method for nickel-based powder metallurgy materials containing Cr is proposed.

[0007] Solve the two problems of low hardness and poor wear resistance of nickel-based materials.

[0008] Technical solution: A method for preparing Cr-containing nickel-based powder metallurgy materials with surface strengthening based on high-current pulsed electron beam, comprising:

[0009] Step 1: Pure chromium powder and pure nickel powder are mixed into Ni-21Cr mixed powder in a mass ratio of 79:21;

[0010] Step 2: Use ball mill to mix and obtain uniform powder;

[0011] Step 3: Press into shape using a mold, and then sinter in a sintering furnace;

[0012] Step 4: The sintered sample is irradiated several times with a high-current pulsed electron beam to obtain a dense surface-reinforced Ni-Cr powder metallurgy sample.

[0013] Furthermore, in step 2, during ball milling, the ball mill jar is filled with stainless steel grinding balls, the mass ratio of stainless steel grinding balls to Ni-21Cr mixed powder is 10:1, and argon is filled in the ball mill jar, and the ball milling is carried out at a speed of 200-300 r / min for 2-3 hours.

[0014] Furthermore, in step 3, the sintering temperature is 1300°C.

[0015] Furthermore, in step 4, the control parameters of each high-current pulse electron beam irradiation treatment are: irradiation acceleration voltage is 27 keV, current pulse duration is 1.5 μs, energy density is 4-6 J / cm 2 The beam spot diameter is 50-60 mm, the pulse interval is 8-10 s, and the irradiation process is carried out in a vacuum of 5×10 -3 In the environment of Pa.

[0016] Furthermore, the number of irradiation times is not less than 15 times.

[0017] Beneficial effects: In the process of the present invention, the surface strengthening treatment is carried out on the Ni-Cr powder metallurgy sample, and an extremely high-energy energy beam is used to instantly act on the surface of the sintered material, so that the surface undergoes a process of sudden heating, extreme cooling and directional solidification at the same time, thereby forming a dense, ultra-fine-grained and uniformly distributed strengthening layer on the surface. The irradiation intensity, number of irradiations, height and other regulatory factors of the electron beam are all key to controlling the formation of a strengthening layer on the sample surface. Among them, the number of irradiations particularly affects the formation of compounds in the alloy layer, thereby affecting the actual performance. At the same time, in the ball milling process before sintering, the ball-to-material ratio, rotation speed, and ball milling time will all affect the preparation quality of the sample. Selecting appropriate ball milling parameters and sample preparation pressure is very critical for the preparation of sintered samples.

[0018] In addition, in the present invention, the mixing ratio of nickel-chromium powder is 79:21, which is higher than the commonly used Cr 20 Ni 80The alloy contains more Cr. Considering the maximum solid solubility of Cr in Ni and the effect of electron beam in improving the solid solubility, the Cr content is appropriately increased to improve the corrosion resistance.

[0019] The method of the present invention is low-cost, short-cycle, highly efficient, and simple to operate, playing an extremely important role in the practical application of nickel-based alloys. It overcomes the main shortcomings of powder metallurgy technology based on conventional powder metallurgy methods, improves sample surface properties, and extends the service life of devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart of the present invention;

[0021] Figure 2 Surface scanning images of Ni-21Cr powder metallurgy samples, where (a) is the original sample, (b) is after 5 electron beam irradiation, (c) is after 15 electron beam irradiation, and (d) is the SEM image after 15 electron beam irradiation;

[0022] Figure 3 is the hardness of the sintered sample and the irradiated sample after sintering. DETAILED DESCRIPTION

[0023] The present invention will be further explained below with reference to the accompanying drawings.

[0024] A method for preparing a Cr-containing nickel-based powder metallurgy material with a surface strengthened by a high-current pulsed electron beam, comprising:

[0025] Step 1: Pure chromium powder and pure nickel powder are mixed in a mass ratio of 79:21 to form Ni-21Cr mixed powder.

[0026] Step 2: Use a ball mill to mix and obtain a uniform powder. Specifically, during ball milling, a ball mill jar is loaded with stainless steel grinding balls. The mass ratio of stainless steel grinding balls to Ni-21Cr mixed powder is 10:1. Argon gas is filled in the jar to prevent oxidation during the milling process. The milling is carried out at a speed of 200-300 r / min for 2-3 hours. In this example, the jar is loaded with 300 grams of stainless steel grinding balls, 23.7 grams of pure nickel powder, and 6.3 grams of pure chromium powder.

[0027] Step 3: Press into shape using a mold, and then sinter in a sintering furnace at 1300°C.

[0028] Step 4: The sintered sample was irradiated several times with a high-current pulsed electron beam to obtain a dense surface-strengthened Ni-Cr powder metallurgy sample. The control parameters of each high-current pulsed electron beam irradiation treatment were: irradiation acceleration voltage of 27 keV, current pulse duration of 1.5 μs, and energy density of 4-6 J / cm 2The beam spot diameter is 50-60 mm, the pulse interval is 8-10 s, and the irradiation process is carried out in a vacuum of 5×10 -3 Pa environment. The irradiation times are not less than 15 times.

[0029] HCPEB irradiation, as an emerging energetic beam surface modification technology, can modify sample surfaces over a wide range to achieve optimal surface properties. Compared to methods such as laser treatment and ion implantation, it offers unique advantages such as high efficiency, strong controllability, and zero contamination in a vacuum environment. HCPEB irradiation can instantly deposit high energy on the sample surface, causing the substrate to melt. Simultaneously, alloying elements penetrate into the molten zone, causing physical changes or chemical reactions. Through rapid cooling and directional solidification, a uniformly distributed alloy layer with unique properties is formed on the substrate surface.

[0030] The electron beam irradiation process is a non-equilibrium state. In the present invention, a supersaturated Ni(Cr) solid solution and an intermetallic compound reinforcement phase are formed. The sample obtained by high temperature sintering in step 3 has a large number of pores on the surface and a grain size of about 26.4 μm. Figure 2 As shown in (a). After 5 times of electron beam irradiation, the surface pores of the sintered sample are slightly reduced and the sample is obviously denser, as shown in Figure 2 As shown in (b). After 15 times of electron beam irradiation, the pores on the sample surface are greatly reduced and the sample is flat and dense, as shown in Figure 2 As shown in (c). Figure 2 (d) shows the SEM image of the slip and ultrafine grain structure formed in certain areas on the surface irradiated 15 times. The size distribution of these ultrafine grains is quite uniform, and their average size can be statistically determined to be about 110 nm (0.11 μm).

[0031] The surface hardness of nickel-chromium after conventional metallurgy sintering is low, at 1.8 GPa. After electron beam irradiation, the surface becomes dense from loose and porous, and the grains are refined. The surface hardness reaches 2.2 GPa after 15 irradiations. Figure 3 As shown in the figure, it can be seen that electron beam irradiation of nickel-chromium sintered samples is an efficient non-equilibrium strengthening method, which can properly compensate for the fatal defects on the surface of sintered materials.

[0032] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing Cr-containing nickel-based powder metallurgy materials based on high-current pulsed electron beam surface strengthening, characterized in that: include: Step 1: Pure chromium powder and pure nickel powder are mixed into Ni-21Cr mixed powder in a mass ratio of 79:21; Step 2: Use ball mill to mix and obtain uniform powder; Step 3: Press into shape using a mold, and then sinter in a sintering furnace; Step 4: The sintered sample is irradiated several times with a high-current pulsed electron beam to obtain a dense surface-reinforced Ni-Cr powder metallurgy sample; In step 2, during ball milling, the ball mill is filled with stainless steel grinding balls, the mass ratio of stainless steel grinding balls to Ni-21Cr mixed powder is 10:1, and the ball mill is filled with argon gas and ball milled at a speed of 200-300 r / min for 2-3 hours; In step 3, the sintering temperature is 1300° C. In step 4, the control parameters of each high-current pulse electron beam irradiation treatment are: irradiation acceleration voltage is 27 keV, current pulse duration is 1.5 μs, energy density is 4-6 J / cm 2 The beam spot diameter is 50-60 mm, the pulse interval is 8-10 s, and the irradiation process is carried out in a vacuum of 5×10 -3 In the environment of Pa; The number of irradiation times shall not be less than 15 times.

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